Host a synchronous launch for larger and longer group projects - break out students into their groups and ask them to complete an icebreaker/get to know each other activity. Perhaps have them assign roles at this time too.

Custom groups - if you can, set up the groups ahead of time. If you cannot, set a break for right before the group session so that you can organize the students into their groups

When you ask students to break into groups to explore something, always ask them to report back on what they found. This adds a layer of accountability and defines an outcome for the group session.